A cage-type structure of silsesquioxane having a siloxane bond as nucleus has both characteristics of an inorganic material and organic material, and has an excellent heat resistance, electrical property, flame resistance, weather resistance, and mechanical properties. Further, different from silica, which is a complete inorganic material, as it is soluble to a general organic solvent, it has a characteristic that it is easy to handle, and has excellent workability including film forming and moldability. Thus, development and research of hybrid materials and nanocomposites of silsesquioxane and high molecular organic compound have been conducted on a global basis.
A cage-type structure of silsesquioxane having α,β-diol group is shown, for example, on the website of Hybrid Plastics (USA) (nonpatent document 1), and it is a cage-type structure of silsesquioxane that has a single α,β-diol group in one molecule, and which molecular level is monodispersed. From its structure, it can be estimated that the synthesis process is complex and involves high cost. Further, as there is one α,β-diol group, it can be also estimated that it is hardly dispersed in a polar organic polymer, in particular, natural polymer and their derivatives.
On the other hand, a cellulose derivative is utilized in various fields as a plastic material derived from biomass. However, as there are drawbacks such as in the molten workability and water resistance when used alone, hybridization with other materials including silicon compounds has been widely considered.
For example, in Japanese Laid-Open Patent Application No. 2002-194228, it has been proposed to compound a sol-gel product of alkoxysilane into a cellulose derivative to decrease the water vapor transmission rate and birefringence rate of the cellulose derivative (patent document 1).
Further, in POLYMER, Volume 35, No. 25, 1994, 5565-5570, it is described to add water and hydrochloric acid to hydroxypropyl cellulose having a weight average molecular weight of 60000 and tetraethoxysilane, to allow hydrolytic polycondensation of tetraethoxysilane, thereby producing a complex of hydroxypropyl cellulose and silica (nonpatent document 2). Further, U.S. Pat. No. 6,275,728 describes a water-absorbing film comprising hydroxypropyl cellulose and silica gel (patent document 2).
However, with these techniques, due to the presence of a large amount of silanol groups in the sol-gel products, the storage stability and workability were not sufficient. Further, those added with a solid silica gel had drawbacks in that as both materials do not form a chemical network structure at a molecular level, the compatibility is insufficient, and the mechanical properties and transparency decrease, and thus the features of both materials could not be exerted sufficiently.
Further, concerning hybrid of a cellulose derivative and silsesquioxane, for example, it is shown on the website of Hybrid Plastics (USA) that by compounding several percent of silsesquioxane into cellulose acetate propionate, the heat resistance and flame resistance can be improved. Further, in Polymer Preprints, 2004, 45(1), 642-643, it is described that by nanocompositing cellulose propionate and silsesquioxane, a transparent molded product having ductility can be obtained, and a composite of a cellulose propionate and silsesquioxane having 3 silanol groups and isobutyl group has a high transparency, showing a significant Tg increase, and that the tensile property is enhanced at room temperature and higher temperature than Tg (nonpatent document 3).
Concerning the transparency, it has been described that even by adding silsesquioxane to these cellulose esters having originally high transparency, the transparency can be maintained.
However, these considerations have been made on cellulose esters, and it has not been known for cellulose ethers.    Patent document 1: Japanese Laid-Open Patent Application No. 2002-194228    Patent document 2: U.S. Pat. No. 6,275,728    Nonpatent document 1: website of Hybrid Plastics [online] [Searched on Aug. 2, 2007]; Internet <URL: http://www.hybridplastics.com/products/frames.html>    Nonpatent document 2: POLYMER, Volume 35, No. 25, 1994, 5565-5570    Nonpatent document 3: Polymer Preprints, 2004, 45(1), 642-643